Serial Cable Guide
for the
CM11 / CM12 / ActiveHome / Macintosh

Introduction

I decided some time ago to make my own adaptor cable so I could use my CM12 interface with my Macintosh.

Over time I made other adaptor cables for other serial devices as well as a complete replacement cable for the CM12 that was longer han the original and didn't require the adaptor stage.

During this time I discovered that there wasn't a really conclusive guide to how this was done. What was worse was the fact that some cables described elsewhere DIDN'T work.

Please enjoy!


The connectors


The data sheets (HWB)

Serial (PC 9)

Also known as EIA/TIA 574

9 PIN D-SUB MALE (at the Computer)

9 PIN D-SUB MALE at the Computer.

Pin Name RS232 V.24 Dir Description
1 CD CF 109 <-- Carrier Detect
2 RXD BB 104 <-- Receive Data
3 TXD BA 103 --> Transmit Data
4 DTR CD 108.2 --> Data Terminal Ready
5 GND AB 102 --- System Ground
6 DSR CC 107 <-- Data Set Ready
7 RTS CA 105 --> Request to Send
8 CTS CB 106 <-- Clear to Send
9 RI CE 125 <-- Ring Indicator

Note: Direction is DTE (Computer) relative DCE (Modem).
Note: RS232 column is RS232 circuit name.
Note: V.24 column is ITU-TSS V.24 circuit name.

Macintosh RS-422

It's possible to connect RS-232 peripheral to the RS-422 port available on Macintosh computers.

Use RXD- as RXD, TXD- as TXD, Ground RXD+, Leave TXD+ unconnected, GPi as CD.

8 PIN MINI-DIN FEMALE (at the computer)

8 PIN MINI-DIN FEMALE at the computer.

Pin Name Dir Description
1 HSKo --> Output Handshake
2 HSKi/CLK <-- Input Handshake or External Clock
3 TXD- --> Transmit Data (-)
4 GND --- Ground
5 RXD- <-- Receive Data (-)
6 TXD+ --> Transmit Data (+)
7 GPi <-- General Purpose Input
8 RXD+ <-- Receive Data (+)

Note: Direction is DTE (Computer) relative DCE (Modem).

Note: GPi is connected to SCC Data Carrier Detect (or to Receive/Transmit Clock if the VIA1 SYNC signal is high). Not connected on the Macintosh Plus, Classic, Classic II, LC, LC II or IIsi.


Connection Table

Letter
DB9 Pin #
mini DIN8 Pin #
RJ 11
Colour Scheme #1
Colour Scheme #2
A
2
5
1
Yellow
-
B
9
2
2
Green
-
C
3
3
3
Red
-
D
5
4, 8 (*)
4
Black
-

(*) I have found on my machines if you do NOT join pin 8 to pin 4 the cable DOESN'T work!


Hints, Tips & Notes

Don't forget! The images here are from the FRONT of the plugs - when you are soldering (behind the plug) things will be back-to-front. Don't muddle your pins!

The pins on mini-DIN8 cables are very fine and can be fiddly to solder - make sure your soldering tip is fine. Extended soldering may cause the pins to move out of position - keep soldering times short or alternatively insert the plug in to an unused (spare) socket (not on your computer!) to keep them in position.

If you're not brave enough to try soldering a mini-DIN8 plug you can always salvage or buy a moulded one from somewhere. Use a multimeter / continuity tester to fing the right wire colour / pin combo. If you use a mini-DIN8 <-> mini-DIN8 serial cable you can cut it in half to make 2 adaptors / leads.

I find that the out sleeves on several mini-DIN8 plugs stop it from going in to the serial port properly (it strikes the case) - to prevent this I usually place a drop of glue or silicone in the sleeve when assembling the plug and pull the outermost section back about 5mm to allow better clearance.

Cable - I have made most of my cables from either flat modular 4 core telephone cable or the round 4 core variety to lengths of about 5m without any problems. If you require better signal immunity in high electrical noise environments (or have serial devices at high speeds) using a 4 cored shielded cable may be wise. I find it easiest to solder the braid / drain wire to the outer metal casing / rim of the plug at each end.

My crimper didn't accept RJ11 plugs - I found you could drive the pins down quite easily with a jeweller's screwdriver


Links

The Hardware Book - a great source of connector pinouts, adaptor cables and more

MouseHouse - the guide I originally used - this cable does NOT seem to work on ANY of my machines! See the note on the connection table above

Shed - The home of the ultimate Mac home automation application "Xtension" - also plenty more info there


Disclaimer

All information here is presented "as is" - no responsibility can be taken for use of this data in any way


©2003 Antony N. Lord